Modern public-switched telephone networks (PSTN) use a signaling protocol, e.g. signaling system No. 7 (SS7) for switching of telephone calls. Signaling messages are transported in a signaling network separate from bearer channels. To enable the transport of SS7 signaling over an internet protocol (IP) based network, the SIGTRAN working group of the internet engineering taskforce (IETF) has defined a set of SIGTRAN protocols. Examples of such protocols are the message transfer part 3 (MTP3) user adaptation (M3UA) protocol or the signaling connection control part (SCCP) user adaptation (SUA) protocol. An interworking between SS7 protocols and user adaptation protocols is performed at a signaling gateway, which generally terminates underlying protocol layers both on the SS7 and the IP side.
There are generally three types of signaling processes defined in SIGTRAN that can use a user adaptation protocol for a transport of signaling messages. These processes are a signaling gateway process (SGP), an application server process (ASP) and an internet protocol server process (IPSP). For a communication between these processes, three different types of interfaces are defined: a SGP to ASP interface, an ASP to SGP interface and an IPSP to IPSP interface. The interfaces are incompatible, as e.g. only certain types of messages are allowed to be sent via a particular interface. The SIGTRAN protocols thus define interfaces which depend on the type of communication process and which are asymmetrical, i.e. for which the direction of communication matters. Details on such protocols can be found in RFC 3868 for the SUA protocol and RFC 4666 for the M3UA protocol.
Accordingly, two SGPs of two different SIGTRAN signaling gateways (SGs) cannot communicate with each other using standard SIGTRAN interfaces. For a communication they need to additionally emulate an ASP role or an IPSP role. Accordingly, they need to be provided with additional resources for enabling such a communication. Similarly, it is not possible for two network nodes comprising ASPs that serve two different application servers to communicate with each other using standard SIGTRAN interfaces unless they additionally implement either a SGP role or an IPSP role. Accordingly, the communication capabilities via the interfaces defined in the SIGTRAN standard are rather limited and may only be improved by providing an additional functionality in the SIGTRAN network nodes. Yet signaling gateways and application servers are often not provided with such an additional functionality, thus preventing certain types of communication.
In the SS7 network several functions are centralized at signaling transfer points (STPs). When migrating to an IP-based network, such centralized functions may be placed in a SIGTRAN signaling gateway. Yet in an all-IP network there is generally no need for a SIGTRAN signaling gateway. The SIGTRAN standards do not define any network nodes capable of performing these centralized functions.
Further, network and traffic management/maintenance functions and procedures are not defined in the SIGTRAN protocols that would enable a simple relay of SS7 signaling in an IP-based network, unless a change of a SIGTRAN adaptation layer protocol is performed at relay. A change of a SIGTRAN adaptation layer at a relay may further have negative consequences due to interactions between layers. For example, a change from M3UA to a message transfer part 2 (MTP2) user peer-to-peer adaptation (M2PA) layer may lead to a negative interaction between MTP3 carried over M2PA and M3UA, which may influence a quality of service provided by M3UA to its users.
Although the SUA standard RFC 3868 mentions a relay functionality, it does not mention how such a functionality may be achieved. A relay functionality is further known from a signaling gateway (SG), which routes messages between the SS7 and the IP network. Yet the SG needs to implement a SS7 layer stack and performs an interworking with the user adaptation layer. A relay is thus only possible at an expense of additional SS7 layers which have to be provided and maintained in the SG. Such a relay functionality again excludes a communication between certain types of signaling processes. An interoperability of the signaling processes cannot be achieved by one of the above-mentioned relay functionalities. A number of possible communication scenarios are thus excluded with such a relay functionality. Without a relay function it is not possible to realize a hierarchical SIGTRAN network architecture based on existing SIGTRAN user adaptation layers. Approaches relying on a change of the adaptation layer at relay complicate the node configuration, network maintenance and increase operational expenditure.
Accordingly, there is a need to overcome or at least mitigate the above-mentioned drawbacks. In particular, there is a need to achieve an improved transport of messages in an IP-based signaling network and to enable a communication between different types of signaling processes over such a network. It is further desirable to achieve such an improved transport of messages without the need to implement SS7 protocol layers in the network nodes of the IP-based signaling network, and accordingly to reduce necessary network maintenance and operational expenditure. Further, there is a need to provide a network entity in an IP-based signaling network capable of performing centralized functions.